Abstract Mutations in the mitochondrial encoded DNA or in the nuclear encoded mitochondrial genes can lead to loss of function phenotypes in mitochondrial proteins1. Mitochondrial diseases (MD) are a heterogeneous group of disorders with several different mutations leading to a variety of organ phenotypes. In general, mitochondrial diseases are characterized by diminished function of organs with high energetic demands, such as the heart, skeletal muscle, and brain2. Additionally, patients with MDs often present with dental disease that requires unique management11. Many anesthetic drugs suppress mitochondrial function, which presents a challenge in the treatment of MD patients12. Patients with MD can develop progressive respiratory failure and lactic acidosis, which are exacerbated with anesthesia13. In addition to dental treatment concerns, manifestations of poor bone heath; such as osteopenia and osteoporosis, have been observed in MD patients. The proposed study aims to discover novel genetic targets that can be pharmaceutically targeted in order to restore function and survival to cells carrying a mitochondrial mutation. A high-throughput small molecule screen on a trans-mitochondrial hybrid (cybrid) model of mitochondrial encephalomyopathy, lactic-acidosis, and stroke-like episodes (MELAS) syndrome was performed to discover compounds that lead to an increase in cell survival in conditions of nutrient deprivation. Doxycycline was identified amongst the top hits. Interestingly, doxycycline was also identified in a high-throughput small molecule screen on Rieske (complex III) mutant fibroblasts and ND1 (complex I) mutant cybrids using the same cell survival assay as the MELAS screen. Across the three independent small molecule survival screens, only two families of compounds were identified as positive hits: antibiotics targeting the mitochondrial ribosome and mTOR inhibitors. mTOR inhibiton has been previously studied in mitochondrial disease3?5, therefore, this project will focus on the efficacy of doxycycline as a therapy in mitochondrial disease. Based off the common screen hits across cell lines, I hypothesize that doxycycline is able promote survival in mitochondrial disease independent of genetic mutation. Further, I believe this is occurring through decreases in mitochondrial protein synthesis, modulation of stress response factors, and inhibition of the cell death pathway. The proposed experiments will first aim to identify the mechanism by which doxycycline promotes cell survival in cells with mitochondrial mutations. Ndufs4 knockout mice, a well-established mitochondrial mutant mouse with strong neuronal deterioration and short lifespan, will be treated with doxycycline to evaluate the efficacy of doxycycline in vivo. The proposed work will lay the groundwork for a novel therapeutic strategy to benefit MD patients. !